JP3387456B2 - Switching power supply - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching power supply having a main switching element and a single or a plurality of sub switching elements which perform on / off operations in synchronization with or on / off of the main switching elements. Regarding the device.

[0002]

2. Description of the Related Art Generally, a switching power supply is widely used to supply a stable DC voltage from a commercial AC power supply to electronic equipment such as electronic calculators and communication equipment. In such a switching power supply device, a main switching element is connected in series to the primary winding of the transformer, and the main switching element is repeatedly turned on / off to intermittently apply the input voltage to the transformer to rectify the rectification connected to the secondary winding. 2. Description of the Related Art Switching power supply devices using various circuit systems such as a forward converter and a flyback converter that obtain a DC output through a smoothing circuit are used. Various types of circuits that improve the characteristics of the circuits are added to these switching power supply devices by adding a circuit including a sub switching element that performs on / off operation in synchronization with or on / off operation of the main switching element. Switching power supply devices have been proposed.

The structure of a conventional switching power supply device having such a sub-switching element will be described with reference to the drawings.

First, the one disclosed in Japanese Patent Laid-Open No. 8-317647 will be described with reference to FIG.

In the figure, reference numeral 50 denotes a switching power supply device, which includes a partial resonance converter circuit 51 and a drive circuit 52. Of these, the partial resonance converter circuit 51
Are capacitors C51, C52, C53, C54, diodes D51, D52, D53, transformer T51, main switching element S51, and sub switching element S5.
It consists of two.

Further, the drive circuit 52 is the output control circuit 5
3, comparators 54 and 55, inverter 56, insulation circuit 5
7, triangular wave oscillator 58, light emitting side photo coupler Pa, light receiving side photo coupler Pb, transistor Q51 and resistor R
51, R52, and R53.

In the thus configured switching power supply device, the sub switching element S52 performs an on / off operation that is the reverse of the on / off operation of the main switching element S51.

Next, the one disclosed in Japanese Patent Laid-Open No. 8-37777 will be described with reference to FIG.

In the figure, reference numeral 60 denotes a switching power supply device, which is a so-called synchronous rectification system which performs rectification using an FET provided on the secondary side of a transformer. This switching power supply device 60 is a transformer T6.
1. Input capacitor C61, FET Q61 as main switching element, FET Q as sub switching element
62, similarly FET Q6 as a sub switching element
3, choke coil L61, output capacitor C62, light emitting side photo coupler PA, light receiving side photo coupler PB, comparators 61, 62, 63, triangular wave oscillator 64, insulation circuit 6
5, 66, an inverter 67, a control circuit 68, and a control signal output circuit 69. Of these, the control signal output circuit 69 includes transistors Q64 and Q65 and resistors R61 to R65.

In the switching power supply device 60 constructed as above, the FET Q62 performs an on / off operation in synchronization with the on / off operation of the FET Q61, and the FET Q6
3 performs an on / off operation that is the inverse of the on / off operation of the FET Q61.

[0011]

However, in each of the above switching power supply devices, the circuit portion for driving the sub switching element is composed of an IC. Further, since the ground level is different between the main switching element and the sub switching element, it is necessary to provide an insulating circuit including photoelectric elements such as a pulse transformer and a photocoupler. As described above, the use of the IC and the pulse transformer has a problem that not only the circuit configuration becomes complicated and the manufacturing cost increases, but also the increase in the number of parts hinders reduction in size and weight.

Therefore, in the present invention, the circuit for controlling the sub-switching element which performs the on-off operation in synchronization with or inversion of the on-off operation of the main switching element does not use an IC and an insulating circuit and is simply constructed. Accordingly, it is an object of the present invention to provide a switching power supply device that realizes cost reduction and reduction in size and weight.

[0013]

In order to achieve the above object, in the present invention, a DC power source, a primary winding and a secondary winding are used.
A transformer having a secondary winding, a main switching element connected in series with the primary winding, and a single or a plurality of single switching elements that perform on / off operation in synchronization with or on / off of the main switching element. In a switching power supply device including a sub-switching element and capable of obtaining a DC output, a sub-switching element drive winding, which is provided in the transformer and generates a voltage for turning on the sub-switching element, and a switch for turning off the sub-switching element. Means and the turn-on of the main switching element.
Or the turn-on trigger
Turn the auxiliary switching element on the winding for driving the switching element.
After a certain time has elapsed after the voltage for
And a time constant circuit for controlling the switching means so as to turn off the ching element .

Further, the switch means comprises a transistor, and the emitter or collector of the transistor is
It is characterized in that the base is connected to the control terminal of the sub-switching element and the base is connected to the time constant circuit.

Further, the time constant circuit comprises a first impedance circuit and a first capacitor charged and discharged by a voltage generated in the auxiliary switching element drive winding.

Further, the impedance value of the first impedance circuit changes according to the DC output or by a signal.

The control terminal of the sub-switching element is connected to one end of the sub-switching element drive winding via a second impedance circuit.

Further, the second impedance circuit is
It is characterized by comprising a second capacitor.

Further, the second impedance circuit is
It is characterized by comprising an inductor.

The impedance value of the first or second impedance circuit changes depending on the direction of the current flowing through the impedance circuit.

Further, it is characterized by further comprising a voltage stabilizing circuit for stabilizing the voltage applied to the time constant circuit.

Further, the voltage stabilizing circuit comprises a Zener diode.

With the above configuration, in the switching power supply device according to the present invention, since the sub switching element is driven by the voltage generated in the sub switching element drive winding of the transformer, the IC, the pulse transformer, and the It is not necessary to provide an insulating circuit composed of a photoelectric element such as a photocoupler, and the number of parts can be reduced, the size and weight can be reduced, and the manufacturing cost can be reduced.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration of a switching power supply device according to a first embodiment of the present invention will be described with reference to the drawings.

In FIG. 1, reference numeral 1 denotes a switching power supply device, which is an application circuit of a circuit generally called a flyback converter, in which the main switching element is repeatedly turned on and off alternately, and when it is on, energy is accumulated and turned off. When, the power is supplied to the load. Further, the switching power supply device 1 employs a so-called active clamp system for clamping a surge voltage applied to the main switching element, and realizes zero voltage switching operation of the main switching element and the sub switching element.

The switching power supply device 1 has a DC power supply E and a transformer T. Here, the DC power supply E may be a rectified and smoothed AC input. Also, the transformer T
Is a primary winding N1, a secondary winding N2, a main switching element drive winding (hereinafter, first drive winding) N3, and a sub switching element drive winding (hereinafter, second drive winding) N4
Have.

Further, the FET as the main switching element
Q1, a primary winding N1 of the transformer T, and a DC power source E are connected in series, and a FET Q2 as a sub switching element.
A series circuit of the capacitor C1 and the capacitor C1 is connected across the primary winding N1 of the transformer T.

Here, the gate of the FET Q1 is connected via a main switching element control circuit (hereinafter, main control circuit) 2 to
It is connected to one end of the first drive winding N3. In addition, FET
The source of Q2 is connected to the drain of the FET Q1, and the gate is connected to one end of the second drive winding N4 of the transformer T via the sub switching element control circuit (hereinafter, sub control circuit) 3.

The gate and source of the FET Q2 are connected via the sub control circuit 3 across the second drive winding N4. Here, the sub-control circuit 3 includes an npn-type transistor Q3 as a switch means, a capacitor C2 as a first capacitor, a resistor R1 as a first impedance circuit, a capacitor C3 as a second capacitor, a resistor R2, and It is provided with beads 4 which is a kind of inductor. The beads include ferrite beads and amorphous beads. Of these, the capacitor C2 and the resistor R1 form a time constant circuit. Further, the capacitor C3, the resistor R2 and the beads 4 are the second
Constitutes the impedance circuit of. In addition, you may use FET as a switch means.

Further, the switching power supply device 1 is provided with a diode D1 as a rectifying circuit and a capacitor C4 as a smoothing circuit on the secondary side of the transformer T.

Next, the operation of the switching power supply device 1 configured as above will be described.

First, at the time of start-up, the FET is turned on via a start-up resistor (not shown) provided in the main control circuit 2.
A voltage is applied to the gate of Q1 to turn on FET Q1. As the FET Q1 is turned on, voltages having the same polarity are generated in the primary winding N1 and the first drive winding N3 of the transformer T, and the FET Q1 is turned on.
Excitation energy is accumulated in the next winding N1.

When the FET Q1 is turned off by the main control circuit 2, the excitation energy stored in the primary winding N1 of the transformer T is released as electrical energy through the secondary winding N2, and the diode D1 and Capacitor C4
Is rectified, smoothed, and supplied to the load.

When all the excitation energy accumulated in the primary winding N1 of the transformer T is released through the secondary winding N2, the first drive winding N3 receives the voltage generated at the start-up. A voltage of the same polarity is generated and the FET Q1 turns on. Thus, with the on / off operation of the FET Q1,
Electrical energy is supplied to the load.

Next, the operation of the FET Q2 will be described. FE
The TQ2 performs an on / off operation that is the reverse of the on / off operation of the FET Q1 in order to reduce the switching loss and the switching surge of the FET Q1.

First, when the FET Q1 is turned off, a voltage having a reverse polarity to the voltage generated when the FET Q1 is turned on is generated in the second drive winding N4. This voltage is applied to the gate of the FET Q2 via the capacitor C3, the resistor R2, and the beads 4 that form the sub control circuit 3, and the FE
TQ2 turns on. Further, the voltage generated in the second drive winding N4 is applied to the capacitor C2 via the resistor R1 forming the time constant circuit, and the capacitor C2 is charged. When the charging voltage of the capacitor C2 reaches the threshold voltage of the transistor Q3, the transistor Q3 turns on. As a result, the potential difference between the gate and the source of the FET Q2 disappears, and the FET Q from the second drive winding N4 is removed.
The application of the voltage to the gate of 2 is interrupted, and the FET Q2 is rapidly turned off.

Here, after the voltage is generated in the second drive winding N4, the charging voltage of the capacitor C2 is changed to the transistor Q.
The time required to reach the threshold voltage of 3 is the time constant of the time constant circuit including the resistor R1 and the capacitor C2.

The on / off operation of the above-mentioned FETQ1 and FETQ2 is shown in FIG.

In the figure, (a) is the drive pulse waveform of the FET Q1, (b) is the gate voltage waveform of the FET Q2, and (c) is the drive pulse waveform of the FET Q2.

Here, the ON period T2 of the FET Q2 is sandwiched from the end of the ON period T11 of the FET Q1 with a dead time dt1 in which both the FET Q1 and the FET Q2 are turned off.
1 starts. In the dead time dt1, the application of the voltage from the second drive winding N4 of the transformer T to the gate of the FET Q2 is suppressed by the resistor R2 and the beads 4, and the FE
This is caused by delaying the turn-on of TQ2.

The delay time of turn-on of the FET Q2 is such that the gate voltage of the FET Q2 is 0V to the FET Q.
This is the time until the threshold voltage Vth of 2 is reached. Therefore, this time is a time in which the input capacitance (capacitance between the gate and the source) of the FET Q2 is charged to the threshold voltage Vth. The slope of the waveform until the gate voltage of the FET Q2 reaches the threshold voltage Vth is the resistance value of the resistor R2, the inductance value of the beads 4, the impedance value of the second impedance circuit determined by the capacitance value of the capacitor C2,
The voltage value generated in the second drive winding N4 and the FETQ
2 is determined by the input capacitance, and the impedance value of the second impedance circuit and the second drive winding N
It is possible to adjust the slope and adjust the length of the dead time dt1 according to the voltage value generated in the No. 4 circuit. Also, F
When the input capacitance of the ETQ2 is small, an external capacitor may be connected between the gate and source of the FETQ2 to form the second impedance circuit.

Further, since the time constant differs depending on the resistance value or the capacitance value of the resistor R1 and the capacitor C2 constituting the time constant circuit, the time constant is selected by selecting the resistor R1 and the capacitor C2. The constant can be adjusted. As a result, the turn-off of the FETQ2 can be accelerated or delayed, and the FETQ2 can be turned off.
The length of the ON period T21 of 2 can be adjusted.

The FET Q1 is turned on from the end of the ON period T21 of the FET Q2 with a dead time dt2 in which both the FET Q1 and the FET Q2 are turned off.

As described above, in the switching power supply device 1, the FET Q1 and the FET Q2 have the dead time d.
Since the on / off operations which are opposite to each other are performed with t1 and dt2 sandwiched between them, there is no risk of loss and element destruction due to simultaneous turning on of these two FETs.

Further, a FET as a sub switching element
Since Q2 is driven by the voltage generated in the second drive winding N4 of the transformer T, it is not necessary to use photoelectric devices such as an IC, a pulse transformer, and a photocoupler, so that the number of parts can be reduced, and the size and weight can be reduced and manufactured. Cost reduction is realized.

When the transistor Q3 is turned on, F
Since the ETQ2 is rapidly turned off, the switching speed is improved, and the switching loss of the FET Q2 is reduced.

Further, the resistor R2 reduces the surge voltage generated between the gate and source of the FET Q2.

The beads 4 reduce the surge current generated between the gate and source of the FET Q2.

Further, the resistor R2 and the beads 4 can suppress the application of the voltage from the second drive winding N4 to the gate of the FET Q2 and delay the turn-on of the FET Q2. Therefore, by adjusting the resistance value or the inductance value of the resistor R2 and the beads 4,
Q2 can be turned on at an appropriate timing.

Further, the direct current is cut by the capacitor C3 as the second capacitor, and the drive loss of the FET Q2 is reduced.

Although the bead 4 is used as the inductor in the above embodiment, another inductor such as a winding coil may be used, or a plurality of inductors may be connected in series. Is.

The configuration of the sub-control circuit for controlling the on / off operation of the FET Q2 is not limited to that described above, and for example,
The ones shown in 3a to 3g of FIGS. 3 to 9 also perform the same operation as the above-mentioned circuit and obtain the same effect. Note that FIG.
9 to FIG. 9 only show the main parts of the switching power supply device, and the same or corresponding parts as in FIG. 1 are designated by the same reference numerals and the description thereof is omitted.

Of these, the sub control circuit 3a shown in FIG.
As shown in FIG. 1, the bead 4 is omitted and the connection point of the resistor R1 is changed.
Is different from the sub control circuit 3 of FIG.

The sub-control circuit 3b shown in FIG. 4 differs from the sub-control circuit 3 of FIG. 1 in that the beads 4 are omitted and the connection point of the resistor R1 is changed.

The sub control circuit 3c shown in FIG.
1 is that the p-type transistor Q31 is used and the arrangement of the capacitor C2 and the resistor R1 is changed accordingly.
Is different from the sub control circuit 3 of FIG.

The sub control circuit 3d shown in FIG. 6 differs from the sub control circuit 3 of FIG. 1 in that a capacitor C5 and a diode D2 are provided.

The sub-control circuit 3e shown in FIG. 7 differs from the sub-control circuit 3d shown in FIG. 6 in that the beads 4 are omitted and the connection point between the resistor R1 and the diode D2 is changed.

The sub control circuit 3f shown in FIG. 8 also differs from the sub control circuit 3d of FIG. 6 in that the beads 4 are omitted and the connection point between the resistor R1 and the diode D2 is changed.

The sub control circuit 3g shown in FIG.
It is a modified example of the sub-control circuit 3d shown in FIG. 3, and uses a pnp-type transistor Q31, and accordingly, the arrangements of the capacitor C2 and the resistor R1 are replaced with each other.
Different from

Next, another modification of the switching power supply device 1 will be described with reference to FIG. It should be noted that the figure shows only the main parts, and the same or corresponding parts as in FIG. 1 are designated by the same reference numerals and the description thereof will be omitted.

In FIG. 10, the sub control circuit 3h has an np
An n-type transistor Q3, a resistor R3, and a photocoupler PC as a variable impedance element are provided. Of these, a part of the photocoupler PC is provided in the control circuit 2a on the secondary side of the transformer. Here, the control circuit 2a has an input terminal S, the output of the switching power supply device 1 is fed back to the input terminal S, and the impedance value of the photocoupler PC is changed according to this output. As a result, the impedance value of the resistor R1 as the first impedance circuit changes.

Here, rather than output feedback,
The impedance value of the photocoupler PC may be changed according to the signal. This is an impedance caused by a signal input to the input terminal S from a control circuit (not shown) of the device body mounting the switching power supply device 1 or a control circuit (not shown) inside the switching power supply device 1. It adjusts the value.

The above-mentioned change in impedance value is
It includes both a case where it slides in a certain numerical range and a case where it switches to any one of a plurality of specific numerical values.

Thus, in the sub control circuit 3h,
By adjusting the impedance value of the photocoupler PC according to the output of the switching power supply device 1 or by a signal, the charging / discharging time of the capacitor C2 can be changed and the turn-off timing of the FET Q2 can be adjusted.

Next, a modified example of such a sub control circuit 3h will be described with reference to FIG.

The sub control circuit 3i shown in FIG.
The difference from h is that a pnp-type transistor Q31 is used, the arrangement of the capacitor C2 is changed, and a resistor R3 is added. The other configurations are the same as those of the sub control circuit 3h, and the description thereof is omitted. The sub-control circuit 3i configured in this manner also operates in the same manner as the sub-control circuit 3h and obtains the same effect.

Here, the first or second impedance circuit forming the sub-control circuit of the switching power supply device according to the present invention is not limited to the one described above, and for example, the one shown in FIGS. 12 to 15 is used. Good. It should be noted that each of FIGS. 12 to 15 shows only a main part, and the same or corresponding parts as those shown in FIGS. 1 to 11 are designated by the same reference numerals and the description thereof will be omitted. .

Of these, the impedance circuit 5a shown in FIG. 12 comprises a resistor R4 and a diode D3 connected in series with each other, and a resistor R5 connected in parallel with these.

Further, the impedance circuit 5 shown in FIG.
b is composed of resistors R4, R5 connected in series with each other and a diode D3 connected in parallel with the resistor R4.

Further, the impedance circuit 5 shown in FIG.
c is composed of a resistor R4 and a diode D3 connected in series with each other, and a resistor R5 and a diode D4 connected in series with each other. Here, the diodes D3 and D4 are arranged opposite to each other.

Further, the impedance circuit 5 shown in FIG.
d is composed of a resistor R4 and a Zener diode ZD which are connected in series with each other.

In the impedance circuits 5a to 5d described above, the resistance differs depending on whether the current flows in the forward direction of the diode or in the opposite direction, and the impedance value changes.

Since the impedance value can be changed in this way, for example, the positive voltage and the negative voltage generated in the second drive winding N4 of the transformer T, or
An optimum impedance value can be set according to the on / off ratio of the FET Q2. Further, the impedance value can be set so that the variation in the ON period of the FET Q2 is minimized with respect to the variation in the ON / OFF ratio of the FET Q1.

In particular, as the second impedance circuit, the one shown in FIGS. 12 to 15 to which either the capacitor C3 or the beads 4 shown in FIG. 1 or both of them are added is used. May be.

In the switching power supply device of the present invention as described above, the zero voltage switching operation is realized in which the main switching element and the sub switching element are turned on when the voltage applied across the main switching element and the sub switching element is 0V.

By the way, since the voltage of the commercial power source differs depending on the country, when the input voltage of the switching power supply device is rectified and smoothed, the input voltage varies greatly depending on the country. When the input voltage fluctuates, the voltage generated in the second drive winding, that is, the voltage applied to the time constant circuit of the sub control circuit fluctuates in proportion to the fluctuation of the input voltage, and as a result, the ON time of the sub switching element changes. Fluctuates.

Then, for example, if the on-time of the sub-switching element is shorter than the time when the energy is emitted from the secondary side, the main switching element cannot release all the charges accumulated in its output capacitance and the like. However, there is a problem that the zero-voltage switching operation is not realized because it is turned on before the voltage across its both ends becomes 0 V, and the switching loss increases. On the contrary, if the ON time of the sub switching element is longer than the energy release time from the secondary side, the circulating current flowing through the main switching element that is not involved in the energy supply increases, and the peak current increases accordingly, resulting in conduction loss. There is a problem that the number increases.

Therefore, another modification of the switching power supply device 1 for avoiding such a problem will be described with reference to FIG. It should be noted that this figure shows only the main parts, and the same or corresponding parts as in FIG. 3 are designated by the same reference numerals and the description thereof is omitted.

In FIG. 16, the sub control circuit 3j comprises a voltage stabilizing circuit 6a which is formed by connecting a resistor R6 and a Zener diode ZD2 in series. One end of the resistor R1 is connected to the connection point of the resistor R6 and the Zener diode ZD2.

With this configuration, the FET
When Q2 is on, the potential at the connection point between the resistor R6 and the Zener diode ZD2 does not become higher than the Zener voltage of the Zener diode ZD2, and maintains a substantially constant value. Therefore, the voltage applied to the time constant circuit composed of the resistor R1 and the capacitor C2 becomes substantially constant, and the charging time of the capacitor C2 does not depend on the voltage generated in the second drive winding N4 and is always almost constant. Become. As a result, even if the voltage generated in the second drive winding N4 changes due to the fluctuation of the voltage of the DC power supply E, that is, the fluctuation of the input voltage, the time until the transistor Q3 is turned on, that is, the ON time of the FET Q2 is almost the same. It can be constant.

After turning off the FETQ2, the FETQ is turned off.
After 1 is turned on, resistor R1 and capacitor C2
A reverse voltage generated in the second drive winding N4 is applied to the time constant circuit configured by, the electric charge charged in the capacitor C2 is discharged, and further charged in the reverse direction. However, since there is the Zener diode ZD2, only the voltage of about 0.6V which is the forward voltage of the Zener diode ZD2 is applied to the time constant circuit regardless of the reverse voltage generated in the second drive winding N4. Not done. Therefore, the capacitor C2 will eventually be charged in the opposite direction at about 0.6V. As a result, the initial potential when the capacitor C2 is charged next can be made constant regardless of the fluctuation of the input voltage. Then, by stabilizing the initial state of the capacitor C2, the charging time of the capacitor C2 is further stabilized.

As described above, the ON time of the FET Q2, which is the sub switching element, can be controlled to be substantially constant regardless of the fluctuation of the input voltage, and the zero voltage switching operation of the main switching element can be realized.

Next, modified examples of the sub control circuit 3j will be described with reference to FIGS. 17 to 24. Each of FIGS. 17 to 24 shows only a main part of the switching power supply device, and the same or corresponding parts as those in FIG. 16 and the referenced drawings are designated by the same reference numerals, and the description thereof will be omitted. Omit it.

Of these, the sub control circuit 3k shown in FIG.
In the sub-control circuit 3c shown in FIG. 5, the beads 4 are omitted and a voltage stabilizing circuit 6b including a Zener diode ZD2 is provided in parallel with a series circuit of a capacitor C2 and a resistor R1.

The sub-control circuit 3m shown in FIG. 18 is similar to the sub-control circuit 3d shown in FIG. 6 except that the beads 4 are omitted and the diode D2 is replaced by a Zener diode Z.
The voltage stabilizing circuit 6c composed of D2 is provided.

The sub-control circuit 3n shown in FIG. 19 is similar to the sub-control circuit 3g shown in FIG. 9 except that the bead 4 is omitted and the diode D2 is replaced by a Zener diode Z.
It is configured by providing a voltage stabilizing circuit 6d composed of D2.

Further, the sub control circuit 3o shown in FIG. 20 is a voltage stabilizing circuit in which the zener diode ZD3 is connected in series in the opposite direction to the zener diode ZD2 in the sub control circuit 3j shown in FIG. The circuit 6e is provided and configured. In this case, the capacitor C2
The zener voltage of the zener diode ZD2 is applied during the charging of the
The difference is that the Zener voltage of D3 is applied. However, the same effect is obtained in that the initial state when the capacitor C2 is charged is stabilized.

Further, the sub control circuit 3p shown in FIG. 21 is a voltage stabilizing circuit in which, in the sub control circuit 3k shown in FIG. 17, the Zener diode ZD2 is connected in series in the opposite direction to the Zener diode ZD2. The circuit 6f is provided and configured.

Further, the sub control circuit 3q shown in FIG. 22 is a voltage stabilizing circuit in which the Zener diode ZD3 is connected in series in the reverse direction to the Zener diode ZD2 in the sub control circuit 3m shown in FIG. It is configured by providing a circuit 6g.

Further, the sub control circuit 3r shown in FIG. 23 is a voltage stabilizing circuit in which the Zener diode ZD3 is connected in series in the reverse direction to the Zener diode ZD2 in the sub control circuit 3n shown in FIG. It is configured by providing a circuit 6h.

Further, the sub control circuit 3s shown in FIG. 24 is provided with a series circuit of the resistor R6 and the diode D5 in parallel with the series circuit of the resistors R6 and R1 in the sub control circuit 3j shown in FIG. .

With this configuration, the resistance R
The electric charge charged in the capacitor C2 through 6 and the resistor R1 is discharged through another path including the diode D5 and the resistor R7. In this case, since the voltage proportional to the voltage generated in the second drive winding N4 is applied to the capacitor C2 only when the capacitor C2 is discharged, the on-time of the FET Q2 is not completely constant, and the input voltage varies. You can change it to some extent.

Incidentally, with the direction of the diode D5 reversed,
A voltage proportional to the voltage generated in the second drive winding N4 may be applied to the capacitor C2 only when the capacitor C2 is charged.

Although the sub control circuit provided with the voltage stabilizing circuit has been described above by showing seven embodiments, the embodiments are not limited to this, and FIGS. Even if each of the sub control circuits shown in 10 and 11 is provided with a voltage stabilizing circuit, the same operational effect can be obtained.

The configuration of the voltage stabilizing circuit is not limited to the one using the Zener diode,
Other configurations are also possible.

Next, the configuration of the switching power supply device according to the second embodiment of the present invention will be described with reference to FIG. In the figure, parts that are the same as or correspond to those in FIG. 1 are assigned the same reference numerals and explanations thereof are omitted.

In FIG. 25, 11 is a switching power supply device generally called a forward converter,
In particular, it adopts a so-called synchronous rectification method in which rectification is performed using two sub switching elements provided on the secondary side of the transformer. In the switching power supply device 11, the main switching element alternately turns on and off, and supplies power to the load when the main switching element is on.

The switching power supply device 11 includes a transformer T.
1. FET Q11 as main switching element, FET Q21 and FET Q2 as sub switching element
2, a main control circuit 2 for controlling the on / off operation of the FET Q11, a diode D11 connected between the source and drain of the FET Q21, a diode D12 connected between the source and drain of the FET Q22, and a first control for controlling the on / off operation of the FET Q21. Sub control circuit 31 and FE
Second sub-control circuit 3 for controlling ON / OFF operation of TQ22
2 is provided. L1 is an inductor as a smoothing circuit, and C10 is a capacitor as a smoothing circuit.

Of these, the transformer T1 is the primary winding N
Primary and secondary winding N2, main switching element drive winding (hereinafter, first drive winding) N3, sub switching element drive winding (hereinafter, second drive winding) N41, and sub switching element drive It has a winding (hereinafter, third drive winding) N42. Further, the FET Q11, the primary winding N1 of the transformer T1, and the DC power source E are connected in series. Also, FE
The gate of TQ11 is connected to one end of the first drive winding N3 via the main control circuit 2. The DC power source E is
A rectified and smoothed AC input may be used.

The gate of the FET Q21 is connected to one end of the second drive winding N41 via the first sub control circuit 31, and the gate of the FET Q22 is connected to the second sub control circuit 3.
2 to one end of the second drive winding N42.

Further, the first sub control circuit 31 includes a transistor Q41 and a resistor R as a first impedance circuit.
11, a capacitor C21 as a first capacitor, a resistor R21, a capacitor C3 as a second capacitor
1 and beads 41. Here, the capacitor C31, the resistor R21, and the bead 41 form a second impedance circuit.

The second sub control circuit 32 includes a transistor Q42 and a resistor R as a first impedance circuit.
12, a capacitor C22 as a first capacitor, a resistor R22, a capacitor C3 as a second capacitor
2, and beads 42. Here, the capacitor C32, the resistor R22, and the bead 42 form a second impedance circuit.

Next, the operation of the switching power supply device 11 configured as described above will be described.

First, with the turn-on of the FET Q11,
The secondary winding N2 is connected to the second drive winding N41 of the transformer T1.
A voltage having the same polarity as that of the voltage generated at is generated. This voltage is applied to the gate of the FET Q21 via the capacitor C31 of the first sub control circuit 31, the resistor R21 and the beads 41, and the FET Q21 is turned on.

The second drive winding N4 of the transformer T1
The capacitor C21 is charged through the resistor R11 by the voltage generated in the transistor 1, and this charging voltage is applied to the transistor Q4.
When the threshold voltage of 1 is reached and the transistor Q41 is turned on, the FET Q21 is turned off.

Here, the time from when the voltage is generated in the second drive winding N41 until the charging voltage of the capacitor C21 reaches the threshold voltage of the transistor Q41, that is, F
The ON period of the ETQ 21 is defined by the resistance value of the resistor R11 and the capacitance of the capacitor C21. Therefore,
By selecting each element used as the resistor R11 and the capacitor C21, the time constant can be adjusted and the ON period of the FET Q21 can be set.

Then, after the FET Q21 is turned off, FE
When TQ11 turns off, the third drive winding N42
Then, a voltage having a polarity opposite to that generated when the FET Q11 is turned on is generated, and this voltage is applied to the gate of the FET Q22 via the capacitor C32, the resistor R22 and the bead 42, and the FET Q22 is turned on. The subsequent operation is similar to that of the first sub control circuit 31.

Here, as the FET Q21, an element whose voltage drop when ON is smaller than the forward voltage drop when the diode D11 is conducting is used, and the FET Q21 is operated almost in synchronization with the rectifying diode D11.
When Q21 is on, almost no current flows through the diode D11. At this time, the FET Q21 operates as a rectifying element. This greatly reduces conduction loss,
It is possible to prevent heat generation of the element and improve power conversion efficiency.

Similarly, for the FET Q22, a rectifier diode D1 is used by using an element whose voltage drop when ON is smaller than the forward voltage drop when the diode D12 is conducting.
By operating in synchronism with 2, the conduction loss can be greatly reduced, the heat generation of the element can be prevented, and the power conversion efficiency can be improved.

In addition to the above effects, in the switching power supply device according to the present embodiment, the same effect as that of the first embodiment can be obtained by the two sub switching element control circuits. The description is omitted.

The two sub-switching element control circuits are not limited to those shown in FIG. 25, but may be those shown in any of FIGS. 5 to 11.

The first and second impedance circuits provided in the two auxiliary switching element control circuits may be those shown in any of FIGS. 12 to 15 and 16 to 24, respectively.

[0113]

According to the switching power supply device of the present invention, by adjusting the time constant of the time constant circuit, the ON period of the sub-switching element can be arbitrarily set, and further, the second impedance circuit can be set. Thus, the turn-on timing of the sub switching element can be adjusted. As a result, both the main switching element and the sub switching element can be turned on and off with a dead time between them turned off, and there is no risk of loss and destruction of the element due to simultaneous turning on.

Further, since the sub-switching element is driven by the voltage generated in the sub-switching element drive winding of the transformer, it is not necessary to provide an IC and an insulating circuit including a photoelectric element such as a pulse transformer or a photocoupler.
A reduction in the number of parts, a reduction in size and weight, and a reduction in manufacturing cost are realized.

Further, when the transistor as the switch means is turned on, the sub switching element is rapidly turned off, so that the switching speed is improved and the switching loss of the sub switching element is reduced.

Further, a FET as a sub switching element
The surge voltage generated between the gate and the source of the FET is reduced by the resistor forming the second impedance circuit connected between the gate of the FET and one end of the auxiliary switching element drive winding.

Further, FET as a sub switching element
The bead or inductor forming the second impedance circuit connected between the gate of the FET and one end of the auxiliary switching element drive winding reduces the surge current generated between the gate and the source of the FET.

Further, by the second impedance circuit,
It is possible to suppress the application of a voltage from the sub-switching element drive winding to the sub-switching element and delay the turn-on of the sub-switching element. Therefore, by adjusting the impedance value of the second impedance circuit, the sub switching element can be turned on at an appropriate timing.

The DC current is cut by the second capacitor forming the second impedance circuit, and the drive loss of the sub switching element is reduced.

Further, since the impedance value of the first impedance circuit changes or switches according to the output of the switching power supply device, by changing the charge / discharge time of the capacitor forming the time constant circuit, the FET
The turn-on timing of Q2 can be adjusted to a value according to the output of the switching power supply device.

Since the impedance value of the first or second impedance circuit changes depending on the direction of the current flowing through the circuit, the positive voltage and the negative voltage generated in the sub-switching element drive winding, or the sub-switching element. The optimum impedance value can be set according to the on / off ratio of the main switching element, and the impedance value that minimizes the fluctuation of the on period of the sub switching element against the fluctuation of the on / off ratio of the main switching element. You can

Further, by providing the sub-control circuit with a voltage stabilizing circuit for stabilizing the voltage applied to the time constant circuit, the on-time of the sub-switching element is controlled to be substantially constant regardless of the fluctuation of the input voltage. Therefore, the zero-voltage switching operation of the main switching element can be realized.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a switching power supply device according to a first embodiment of the present invention.

FIG. 2 is a waveform diagram showing an operation of the switching power supply device of FIG.

FIG. 3 is a circuit diagram showing a modified example of the switching power supply device of FIG.

FIG. 4 is a circuit diagram showing another modification of the switching power supply device of FIG.

5 is a circuit diagram showing still another modification of the switching power supply device of FIG.

FIG. 6 is a circuit diagram showing still another modification of the switching power supply device of FIG.

FIG. 7 is a circuit diagram showing still another modification of the switching power supply device of FIG.

FIG. 8 is a circuit diagram showing still another modification of the switching power supply device of FIG.

FIG. 9 is a circuit diagram showing still another modification of the switching power supply device of FIG.

FIG. 10 is a circuit diagram showing still another modification of the switching power supply device of FIG.

FIG. 11 is a circuit diagram showing still another modification of the switching power supply device of FIG.

FIG. 12 is a circuit diagram showing still another modification of the switching power supply device of FIG.

FIG. 13 is a circuit diagram showing still another modification of the switching power supply device of FIG.

FIG. 14 is a circuit diagram showing still another modification of the switching power supply device of FIG.

15 is a circuit diagram showing still another modification of the switching power supply device of FIG.

16 is a circuit diagram showing still another modification of the switching power supply device of FIG.

FIG. 17 is a circuit diagram showing still another modification of the switching power supply device of FIG.

FIG. 18 is a circuit diagram showing still another modification of the switching power supply device of FIG.

FIG. 19 is a circuit diagram showing still another modified example of the switching power supply device of FIG.

20 is a circuit diagram showing still another modification of the switching power supply device of FIG.

FIG. 21 is a circuit diagram showing still another modification of the switching power supply device of FIG.

22 is a circuit diagram showing still another modification of the switching power supply device of FIG.

FIG. 23 is a circuit diagram showing still another modification of the switching power supply device of FIG.

FIG. 24 is a circuit diagram showing still another modification of the switching power supply device of FIG.

FIG. 25 is a circuit diagram showing a switching power supply device according to a second embodiment of the present invention.

FIG. 26 is a circuit diagram showing a conventional switching power supply device.

FIG. 27 is a circuit diagram showing another conventional switching power supply device.

[Explanation of symbols]

1, 11 ... Switching power supply device 2 ... Main switching element control circuits 3, 3a, 3b, 3c, 3d, 3e, 3f, 3g, 3
h, 3i, 3j, 3k, 3m, 3n, 3o, 3p, 3
q, 3r, 3s, 31, 32 ... Sub switching element control circuit 4 ... Beads 6a, 6b, 6c, 6d, 6e, 6f, 6g, 6h ... Voltage stabilizing circuits C2, C21, C22 ... First capacitor C3, C31, C32 ... Second capacitor E ... DC power supply N1 ... Primary winding N2 ... Secondary winding N3 ... Main switching element drive windings N4, N41, N42 ... Sub switching element drive windings Q1, Q11 ... FET ( Main switching element) Q2, Q21, Q22 ... FET (sub switching element) Q3, Q31, Q41, Q42 ... Transistors R1, R11, R12, 5a, 5b, 5c, 5d ... First
Impedance circuits R2, R21, R22, 5a, 5b, 5c, 5d ... Second
Impedance circuit T, T1 ... Transformer

Front page continuation (58) Fields surveyed (Int.Cl. ⁷ , DB name) H02M 3/28 H02M 3/338 H03H 7/06

Claims (10)

(57) [Claims] 1. A DC power source, a transformer having a primary winding and a secondary winding, a main switching element connected in series with the primary winding, and an ON / OFF operation of the main switching element. Alternatively, in a switching power supply device having a single or a plurality of sub-switching elements that perform an on / off operation by being inverted, a sub-source that is provided in the transformer and that generates a voltage that turns on the sub-switching elements. A switching element drive winding, a switch means for turning off the sub switching element, and a turn off or turn on of the main switching element.
To the sub-switching element drive winding
A voltage is generated to turn on the sub switching element.
After a predetermined time, the sub switching element is turned
A switching power supply device comprising a time constant circuit for controlling the switching means so as to turn off . 2. The switch means comprises a transistor, the emitter or collector of the transistor is connected to the control terminal of the sub-switching element, and the base is
The switching power supply device according to claim 1, wherein the switching power supply device is connected to the time constant circuit. 3. The time constant circuit comprises a first impedance circuit and a first capacitor charged and discharged by a voltage generated in the sub-switching element drive winding. Alternatively, the switching power supply device according to 2. 4. The switching power supply device according to claim 3, wherein the impedance value of the first impedance circuit changes according to the DC output or by a signal. 5. The control terminal of the sub-switching element,
It is connected to one end of the auxiliary switching element drive winding through a second impedance circuit,
The switching power supply device according to claim 1. 6. The second impedance circuit comprises a second impedance circuit.
6. A capacitor according to claim 5, characterized in that
The switching power supply device according to. 7. The switching power supply device according to claim 5, wherein the second impedance circuit includes an inductor. 8. The switching power supply device according to claim 3, wherein an impedance value of the first or second impedance circuit changes depending on a direction of a current flowing through the impedance circuit. . 9. The switching power supply device according to claim 1, further comprising a voltage stabilizing circuit that stabilizes a voltage applied to the time constant circuit. 10. The switching power supply device according to claim 9, wherein the voltage stabilizing circuit includes a Zener diode.